The goal of this clinical trial is to learn whether transcranial direct current stimulation (tDCS), a non-invasive brain stimulation, can reduce "craving" and problematic levels of social media/internet use in university students.

The main questions it aims to answer are:

• Does active tDCS reduce craving to use social media during the intervention period compared with sham stimulation and no stimulation?
• Does active tDCS reduce internet/social media addiction severity (measured with the Internet Addiction Test, IAT) compared with sham stimulation and no stimulation, and are any effects still present at follow-up? Researchers will compare three groups-active tDCS, sham tDCS (a simulation where stimulation is stopped after the first seconds), and a control group (no stimulation)-to see whether changes are due to tDCS rather than placebo effects or time.

Participants will:

• Complete an initial screening and baseline questionnaires (a sociodemographic questionnaire and the IAT).
• Be randomly assigned to one of three groups: active tDCS, sham tDCS, or control (no stimulation).
• Complete the IAT again after the intervention and again about 5 weeks later (follow-up), along with questions about social media use habits.

During intervention, participants in active tDCS and sham tDCS will:

• Attend 10 sessions over 2 consecutive weeks (Monday-Friday), with each session lasting about 30 minutes; mobile phone use is not allowed during sessions.
• Rate craving on a Visual Analogue Scale (VAS) at the start and end of each session.

This study will be conducted with university students in the Greater Lisbon area and will follow double-blind procedures for the active vs sham conditions (participants and researchers will not know the assigned condition until the end of the study).

This study investigates whether non-invasive neuromodulation using transcranial direct current stimulation (tDCS) can reduce craving and problematic social media/internet use in university students. The rationale for the study is that excessive and compulsive social media use has been associated with negative mental health outcomes, and behavioral addictions may share neurobiological features with substance addictions, including reward-circuit involvement and reduced inhibitory control. Because tDCS can modulate cortical excitability, often targeting prefrontal areas involved in executive control, this project evaluates whether repeated tDCS sessions can help reduce craving and improve digital self-regulation in individuals with moderate-to-severe problematic use.

Study design and setting The study uses an experimental, double-blind design to strengthen internal validity by reducing expectation and observer bias. Recruitment and data collection will be carried out with university students from the Greater Lisbon area, and study activities will take place in a controlled setting with supervision by the research team. The study is planned as a quantitative, applied primary research project.

Participants and eligibility criteria The sample will be non-probabilistic and recruited by convenience among university students in the Greater Lisbon area. Eligible participants must be 18 years of age or older, available for all study phases, and score 31 or higher on the Internet Addiction Test (IAT), indicating moderate-to-severe dependence.

Participants will be excluded if they have had recent psychopharmacological changes (use or dose change within the last 3 months), a history of dizziness or seizures, a current need for hospitalization or psychotherapy, or diagnoses such as depressive, anxiety, or bipolar disorders with recent symptoms, schizophrenia, other psychotic disorders, or autism spectrum disorder. Additional exclusions include contraindications to tDCS, such as pregnancy, metallic implants, tumors, prior brain surgery, or significant anatomical brain changes.

Recruitment and informed consent Recruitment will occur through in-person informational sessions, where study objectives will be presented and a QR code will be provided for enrollment. Outreach will also be supported through social media and flyers in institutions in the Greater Lisbon area. Interested individuals will provide informed consent and complete an initial sociodemographic questionnaire and the IAT as part of screening/baseline assessment.

Group allocation and masking After recruitment, participants will be randomly allocated to one of three groups: (1) active tDCS, (2) sham stimulation, or (3) control without stimulation, and then contacted via email. The sham condition is designed to mimic the sensation of stimulation to help control for placebo effects. Double-blinding will be implemented for the active vs sham conditions, with coded accounts ("real" and "sham") created to ensure the research team does not know condition assignments until the study ends. The control group does not receive stimulation.

Intervention (tDCS) and device The intervention consists of 10 consecutive sessions delivered over two weeks (Monday to Friday), with each session lasting approximately 30 minutes and following recommended safety parameters. Sessions will be supervised by the research team in a controlled environment, and mobile phone use will be prohibited during sessions.

Stimulation will be delivered using the PlatoWork tDCS Headset, a certified non-invasive neuromodulation device, controlled through the PlatoApp, which guides positioning and helps prevent configuration errors. Electrode positioning will follow the International 10/20 system, with the anode placed at F4 (right dorsolateral prefrontal cortex) and the cathode at F3 (left dorsolateral prefrontal cortex).

Measures and outcomes Data will be collected using a sociodemographic questionnaire, the Internet Addiction Test (IAT), and a Visual Analogue Scale (VAS) for craving. The sociodemographic questionnaire will be used to characterize the sample and verify inclusion/exclusion criteria, including variables such as age, sex, psychotropic medication use, pregnancy status, recent therapies, psychological diagnoses, and presence of metallic implants; it also includes questions on social media habits (daily time, frequency, and typical moments of use).

The IAT is a 20-item self-report Likert-scale measure (0-5), with a total score ranging from 0 to 100; higher scores indicate greater dependence/problematic use. Craving will be measured with a VAS consisting of a 10 cm line anchored from 0 (no desire) to 10 (extremely strong desire).

Craving (VAS) will be assessed twice per stimulation session: at the beginning of each session (baseline craving for that session) and at the end of each session (post-stimulation craving). The IAT and social media habit questions will be administered again after the intervention period and again at follow-up approximately five weeks later to evaluate potential cumulative and sustained effects.

Study procedure and timeline After baseline screening and enrollment, participants will attend the intervention period (10 sessions across two weeks) according to their assigned group (active tDCS, sham, or control). Participants in the stimulation arms will complete craving ratings at the start and end of each session. After the two-week intervention, participants will repeat the IAT and usage-habit questions. Five weeks after the intervention, participants will complete follow-up measures (IAT and usage-habit questions). After completion of the study, a debriefing will be conducted, and participants in the sham and control groups may be offered the real tDCS protocol.

Data management and statistical analysis Data will be extracted from the instruments, organized in digital databases, and analyzed using IBM SPSS Statistics (version 30), with procedures to ensure anonymization and confidentiality. Each participant will be identified only by a numeric code. Analyses will compare changes in craving and dependence across three time points (pre, post, and follow-up) and across groups (active, sham, control).

A repeated-measures MANOVA is planned to test group effects, time effects, and group × time interactions across dependent variables, followed by univariate repeated-measures ANOVAs and post-hoc tests with correction for multiple comparisons when appropriate. The significance level will be set at p < .05.

Ethical considerations and participant safety Participation will be voluntary, and all participants will receive clear information about study objectives, procedures, risks, benefits, and data handling before providing written informed consent. Participants may refuse or withdraw at any time without consequences and may request deletion of their data at any stage.

All data will be pseudonymized using numeric codes, and the code-key linking identities to study codes will be stored separately in an encrypted, password-protected file accessible only to the research team. Data will be stored in a secure institutional digital environment (OneDrive). The PlatoApp associated with the PlatoWork headset does not collect personal information; it records only technical session data (e.g., date, time, duration, intensity) without individual identification.

tDCS is described as a safe and non-invasive technique with typically mild, temporary side effects such as tingling, mild skin discomfort, or mild headache; any adverse effects will be recorded and evaluated, and medical referral may be arranged if needed. Equipment will be sanitized between uses, and conductive sponges will be dedicated to each participant. Participants showing signs of emotional or psychological fragility may be advised to discontinue and may be referred for psychological support at the university psychology clinic.

Inclusion Criteria:

• Age ≥18 years.
• Availability to participate in all study phases/sessions.
• IAT score ≥31 (moderate to severe level).

Exclusion Criteria:

• Diagnosis of depressive, anxiety, or bipolar disorders with recent symptoms; schizophrenia; psychotic disorders; or autism spectrum disorder.
• Recent psychotropic medication use or dose change within the last 3 months.
• Current need for inpatient care or ongoing psychotherapy.
• History of dizziness or seizures/convulsions.
• Contraindications to tDCS, including pregnancy, metallic implants, tumors, prior brain surgery, or significant anatomical brain alterations.

Active vs sham conditions are double-blind using coded accounts ("real" and "sham") so participants and the research team do not know assignment until study completion; the control group receives no stimulation.