Contraindications to donation are temporary and absolute. Any temporary contraindications can become absolute if the temporary ones drag on for a long time.
Let me explain with an example. They used it once - it disappeared from the body after some time - you can donate blood. If you use it regularly - everything is removed from the body longer - you can't donate blood, often never.
If the drugs that he uses do not change the composition of the blood and, upon examination, the donor does not arouse suspicion from the therapist, then in principle it can.