After experimenting for a while, I realized you can´t mix anything resembling an ECA stack (Ephedrine, Caffeine, Aspirin), which used to be very popular as a pre-workout or fat burner, with over-the-counter products.
The only over-the-counter medication containing Ephedrine is Wick MediNait, a cough syrup. Problems with that: It contains 19% Alcohol, so you will get moderately drunk to even feel the Ephedrine. You need to chug at least half a bottle and that might cause nausea (which can actually help for training, but it lasts for hours). A bottle costs 19.50€, so it´s not realistic to use this as a pre-workout.
Next, I looked at replacing Ephedrine with Pseudoephedrine, which, as the name implies, is almost the same compound. It is only marketed against nasal congestion, and unfortunately that´s all it does, unlike the stimulant Ephedrine. I´ve taken more than the daily recommended dose within an hour plus 400 mg Caffeine and didn´t feel anything.
However, Caffeine is still a great pre-workout, I recommend 200-500 mg (200 for women, 500 if you think heart palpitations help you lift more) an hour before a workout.
Aspirin doesn´t really boost your performance, but it can prevent blood clots, the dose recommended for that is about 0.2 – 0.5 pills. Yeah, I´m not gonna cut pills into 5 pieces.
If you are going to be doing a training session with short rest times and lots of sets, don´t take any vasoconstrictors, such as nicotine, amphetamines or caffeine, because you will get ill or burn out. Use vasodilators instead, such as Citrulline or Glycerol. Consider creatine monohydrate.
For maximal strength or a workout with few sets, chug caffeine. Tongkat Ali might also help. Those are the legal options. Only consume stimulants before workouts, not more often than 2-3 days a week.