This study is a drug trial of ethosuximide as a painkiller if you develop pain as a side effect of chemotherapy. Ethosuximide will be compared against placebo (an inactive substance) to test whether any response is a true effect of the drug, and not a 'placebo effect'.

Inclusion Criteria:

• Age >/= 18
• Diagnosis of cancer
• Willing and able to give informed consent to the CIN-E study and complete study questionnaires, this involves adequate understanding of written and spoken English (translators will not be used)
• Chemotherapy-induced painful peripheral neuropathy as diagnosed by score of >12 on the Leeds Assessment of Neuropathic Symptoms and Signs (S-LANSS) with a pain intensity rating of >4, on a 11 point numeric rating scale (0= no pain, 10= worst possible pain).
• Duration of chemotherapy-induced painful peripheral neuropathy >4 weeks. Participant may either have completed chemotherapy, or be receiving ongoing chemotherapy.
• Able to attend research centre according to the required visit schedule.
• Diet allows bovine gelatine (present in both ethosuximide and placebo capsules)
• Women of child-bearing potential must be using a reliable form of contraception i.e. oral contraceptives, a barrier method (condom or diaphragm), intra-uterine device or abstinence.

Exclusion Criteria:

• Renal impairment (serum creatinine >1.5x normal level)
• Deranged liver function (AST>3x normal level)
• Patients currently taking any anti-depressant medication, for example fluoxetine, paroxetine, citalopram, venlafaxine, amitriptyline, or within the past week.
• Patients currently taking any other anti-epileptic drug, including gabapentin, or within the past week.
• Pregnancy
• Allergy to succinimides, ethosuximide, methsuximide, phensuximide. Pre-exisitng painful peripheral neuropathy of any other cause.