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Cycloserine is a chemically synthesised antibiotic substance. It is classified under the Anatomical Therapeutic Chemical (ATC) code J04AB01, a group of drugs used against tuberculosis. The substance appears in the EU Clinical Trials Information System under the registry name CYCLOSERINE, with product names including D-Cycloserine 100 mg.[2][1] Cycloserine is already authorised as a medicine, with an authorisation record held under number XI PL 45043/0109 and authorisation holders including Neon Healthcare Limited and Uppsala University Hospital.[2][1] In the two trials listed here, cycloserine is the test substance, meaning it is the active medicine being investigated.[2][1]
The registry data provided does not include a molecular mechanism of action for cycloserine. As an antibiotic classified under ATC code J04AB01, it belongs to the group of medicines used against tuberculosis bacteria. The supplementary sources describe its use in tuberculosis treatment but do not explain the molecular target in patient terms. The current depression trials investigate whether cycloserine can enhance the effect of transcranial magnetic stimulation, a form of brain stimulation, but the biological reason for this possible effect is not stated in the provided sources.
Cycloserine is given by mouth as a hard capsule. The trials use 100 mg and 125 mg capsules taken orally.[2][1] A WHO-prequalified product described in the supplementary sources is a 250 mg hard capsule for oral use, stored below 30°C in a dry place.[3] The placebo capsules used in the trials are matched in appearance to the active capsules to keep the studies blinded.[2][1]
Two Phase 2 interventional trials are registered. Both are currently authorised, meaning they have received approval to proceed. The first trial, AIDA-DEP (EU CT number 2025-521686-27-01), plans 105 participants and tests 100 mg D-cycloserine added to a nine-weekday course of accelerated intermittent theta-burst stimulation (aiTBS).[2] The second trial, TMSxDCS (EU CT number 2025-521166-95-00), plans 48 participants and tests 125 mg D-cycloserine added to a single day of accelerated transcranial magnetic stimulation (TMS).[1] Both are randomised, placebo-controlled and double-blind, meaning neither participants nor assessing staff know who receives the active drug.[2][1]
Both trials measure depressive symptoms using the Montgomery-Åsberg Depression Rating Scale (MADRS), a standard clinician-rated scale for depression. The AIDA-DEP trial compares the change in MADRS total score from baseline to Day 28 after the first treatment day, rated by a blinded external rater via video consultation.[2] The TMSxDCS trial measures the percentage reduction from baseline MADRS score weekly for six weeks after treatment.[1]
The AIDA-DEP trial enrols adults over 18 years old with a current depressive episode and a MADRS score above 19.[2] The TMSxDCS trial enrols adults with major depressive disorder; the registry entry does not provide further age or score details.[1] Both trials are multicentre and placebo-controlled.[2][1]
The supplementary source on cycloserine-containing regimens in multidrug-resistant tuberculosis reports that the study evaluated efficacy and safety, but the provided extract does not list specific side effects.[4] The WHO labelling source does not list side effects in the provided extract.[3] The trial registry records do not report side effect data.
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