If only getting one, get Selank.
Both had a noticeable effect, with taking Semax first thing in the morning, i felt it clearly riding my motorbike to work through heavy traffic.
I could easily concentrate on more hazards and felt sharper and better focused.
But the general feeling of well-being and calm with Selank so pleasant.
You can take both, but it is not recommended to use at exactly the same time, as they have different and somewhat competing effects. Calm vs focused.
Can recommended both.

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