Individuals receive drug (stimulant, or sedative) on two separate occasions and placebo on two separate occasions. Individuals receive drug in only one room.

Individuals receive drug (stimulant, or sedative) on two separate occasions and placebo on two separate occasions. Individuals receive drug in both rooms.

Drug conditioning is assessed by pairing drug administration with a given context.

The amount of time spent in the two testing rooms is assessed during a 10min exploration test conducted at the orientation session (pre-test) and again at the testing session (post-test). Between the pre- and post-tests, participants complete 4 drug administration sessions; 2 with 20mg MA, 2 with 0mg MA. The Paired Group always receives 20mg MA in the room they spent the least time in at pre-test, and 0mg MA in the other room. The Unpaired Group receives 20mg MA and 0mg MA once in each room. The research question is whether the Paired Group spends significantly more time in the room paired with 20mg MA in comparison to the Unpaired Group. Thus, the outcome measure is the difference in time spent in the room paired with drug administration (i.e. the room that they spent the least time in at pre-test) between pre- and post-tests (i.e., post-test time spent - pre-test time spent) which is compared between the groups. NOTE: Time spent is NOT obtained during drug administration sessions.

Self-reported drug effects are measured using standardized questionnaires 30min before capsule administration (baseline) and at 30min intervals after capsule administration for 4h during each drug administration session. The peak change from baseline is calculated for each session and averaged across drug and placebo sessions. A net difference is calculated by subtracting the mean peak change from baseline during placebo sessions from the mean peak change from baseline during drug (20mg MA) sessions.

Outcome measure: Subjective stimulation (i.e., feeling alert, aroused, energetic) is measured using the Amphetamine scale of the Addiction Research Center Inventory. Scores range from 0-11 with greater scores indicating greater drug effects.

Individuals receive drug (stimulant, or sedative) on two separate occasions and placebo on two separate occasions. Individuals receive drug in only one room.

Paired: Drug conditioning is assessed by pairing drug administration with a given context.

Stimulant or sedative: CS+ for paired, CS0 for unpaired

Placebo: CS- for paired, CS0 for unpaired

The amount of time spent in the two testing rooms is assessed during a 10min exploration test conducted at the orientation session (pre-test) and again at the testing session (post-test). Between the pre- and post-tests, participants complete 4 drug administration sessions; 2 with 20mg MA, 2 with 0mg MA. The Paired Group always receives 20mg MA in the room they spent the least time in at pre-test, and 0mg MA in the other room. The Unpaired Group receives 20mg MA and 0mg MA once in each room. The research question is whether the Paired Group spends significantly more time in the room paired with 20mg MA in comparison to the Unpaired Group. Thus, the outcome measure is the difference in time spent in the room paired with drug administration (i.e. the room that they spent the least time in at pre-test) between pre- and post-tests (i.e., post-test time spent - pre-test time spent) which is compared between the groups. NOTE: Time spent is NOT obtained during drug administration sessions.

Video recordings of the exploration tests (used to calculate time spent) were unavailable (corrupted) for at least one test (pre- or post-) for 3 Paired participants and 2 Unpaired participants. Thus, the participant numbers for this analysis are reduced in comparison to the total number of participants who completed the study.

Participants completed two drug administration sessions with 20mg methamphetamine.

Self-reported side effects: At 30min intervals following drug administration (for 4h), they reported any side effects on a paper and pencil form. Drug side effects (Blurred vision, Dry mouth, Headache, Nausea, Heart racing, Shortness of breath, Dizziness/faintness, Restlessness, Chest discomfort, Shakiness or trembling (legs, arms, hands, feet), Pain or numbness in fingers or toes, Anxiety/tension) were each associated with a 100mm visual analogue scale anchored at the left hand side with "None" and at the right hand side with "Extreme". Participants placed a vertical line bisecting the scale that corresponded with how they were feeling at that time. Scores ranged from 0-100, with higher scores indicating more severe side effects.

Cardiovascular Measures: Heart rate (bpm) and blood pressure mmHg) were monitored using a monitor 30min before drug administration (baseline) and at 30min intervals (for 4h) following drug administration.

Serious adverse events were defined as any side effects reported in the "severe-extreme" range (i.e., >60) or any occasion when the study physician was consulted about high cardiovascular measures.

Serious adverse events are reported for all participants who completed the study (N=109).

The physician was consulted on one occasion regarding high heart rate and blood pressure values in a participant after receiving 20mg MA. The participant reported no additional adverse effects and after resting, heart rate and blood pressure reduced.