Semax vs Selank: what the studies show

Semax and Selank are both synthetic seven-amino-acid peptides that came out of Russian research, and neither has strong human evidence behind it. Semax has more studies, mostly small ones in stroke and eye disease. Selank has a handful of small anxiety studies, and neither has a large, blinded, placebo-controlled trial in our records.^[1][2][3][4]

What they are

Semax is an analogue of the ACTH 4-10 fragment that lacks ACTH's hormone activity. FDA says it is a registered drug in Russia, sold as 0.1% and 1% nasal drops.^[5][6]

Selank is an analogue of tuftsin, a natural short fragment of the human IgG antibody heavy chain. It was developed at the Institute of Molecular Genetics of the Russian Academy of Sciences and is described as an anxiolytic.^[7][8]

In the US, neither is an approved drug. FDA says semax is marketed through wellness clinics and online sellers, and an FDA warning letter states selank is not a component of any FDA-approved human drug.^[5][9]

What the human studies cover

The two peptides were studied for different problems.

Semax:

• In acute stroke, 30 patients given semax with intensive therapy were compared with 80 controls. The authors reported some influence on recovery rate, especially of motor deficits. The abstract does not describe blinding or randomisation.^[1]
• In 110 patients after ischaemic stroke, semax was associated with higher plasma BDNF and better Barthel scores. The abstract does not mention a placebo.^[10]
• In optic nerve disease, the authors reported better visual acuity, visual field and colour vision. Group sizes are not given.^[2]
• In a 27-patient open-label trial in motor neuron disease, semax did not change the course of muscle denervation or clinical scores.^[11]

Selank:

• In 62 patients with generalised anxiety disorder and neurasthenia, 30 got selank and 32 got medazepam. The authors reported similar anxiolytic effects. There was no placebo arm in the abstract.^[3]
• In a study of 40 patients given selank plus phenazepam and 30 given phenazepam alone, the benefit appeared earlier with selank added, and side-effects were lower. This shows an add-on effect, not selank on its own.^[4]
• A comparison of selank and phenazepam in 60 patients reported pronounced anxiolytic effects. The abstract does not say whether patients were randomised.^[12]

The four selank patient studies all appeared in one Russian journal from overlapping author teams, and their abstracts give no dose or route.^{[3][4][12][13]}

One study did put both peptides side by side. In 52 healthy volunteers given selank, semax or placebo, brain scans showed altered connectivity between the right amygdala and temporal cortex after dosing. This is an imaging measure, not a clinical effect.^[14]

Safety and what regulators say

For semax, FDA found no human pharmacokinetic studies by any route and no safety data for subcutaneous use. It also found no published literature on giving semax by subcutaneous injection, one of the forms sold in the US.^[5]

FDA raised a bleeding concern because one report discussed possible antithrombotic properties. It also raised an abuse-potential concern, because semax raised amphetamine-driven dopamine release in rat striatum.^[5][15]

In patients with brain injury after oxygen deprivation, EEG showed episodes of paroxysmal activity after semax injection in some cases.^[16]

For selank, FDA says compounded selank acetate may carry immune-reaction risk from aggregation and impurities. It also says it lacks important information on safety in humans.^[17]

A 2017 study found anticoagulant effects of selank. Effects on clotting in people are not described in our records.^[18]

Both peptides were on FDA's category 2 list of nominated-but-withdrawn substances, current as of 2026-04-22 for selank and 04/22/2026 for semax.^[17]

FDA's briefing document for the July 23-24, 2026 advisory committee proposed not adding semax to the 503A bulks list. It said only two references were available, with too little detail, and that they showed a lack of effectiveness.^[5]

ABC News reportedly said the committee narrowly voted to recommend adding semax and five other peptides, against FDA staff advice. This is a secondary report, and the vote is advisory and non-binding.^[19]

Selank had no FDA briefing document of its own in our records for that meeting.^[20]

Animal work and user reports

In our records, 45 of the 56 animal studies of selank list at least one author from a small, overlapping set.^{[21][22][23][24]}

In rodents, FDA's reviewers summarised semax work as showing neuroprotective effects, pain relief and anxiety-reducing effects, all through poorly understood mechanisms.^[5]

In mice, selank at 300 µg/kg/day for 5 days had anxiolytic effects only in the more anxious BALB/c strain.^[8]

User reports are anecdotal and not clinical evidence. For selank, about 19% of 127 first-hand Reddit reports mentioned less anxiety, and about 12% reported no noticeable effect.^[25]

For semax, about 12% of 127 reports mentioned better focus, and about 12% reported no noticeable effect.^[25]

Used together

FDA notes semax products are offered online alone and in combination with selank. No study of the combination in patients is in our records.^[20]

The bottom line

Semax has small, mostly Russian studies in stroke and eye disease. Selank has small anxiety studies that compared it with, or added it to, benzodiazepine-type drugs.^[1][3][4]

Neither has a large, blinded, placebo-controlled trial in our records.^{[1][10][11][3][12]} Whether selank works for anxiety in a placebo-controlled trial is unknown.^[3][12]

FDA found no human pharmacokinetic studies of semax by any route. It also says it lacks important information on selank safety in humans.^[5][17]

This is a summary of what studies and regulators say, not advice on whether to use either peptide.