The potions used in Asterix comic books resemble the methamphetamine usage of World War II. Has the drug culture within the comics ever been discussed?
No. Asterix is very far from any drug culture, and from methamphetamine usage during war.
Magic potions are older than print. They appear in Greek mythology, for example (Jason puts the dragon to sleep with a potion, Circe turns men into swine with a potion, not to mention love potions). I can't name a potion that grants strength or invincibility, but I put this down to my unfamiliarity with mythology: it's hardly such a far-fetched idea that it could only arise from a direct real-world source of inspiration.
The effect of the magic potion in Asterix is very different from methamphetamine. The magic potion has a purely physical effect: it primarily grants superhuman strength, and also cures some ailments that make one weak. It does not have a direct effect on mood. Characters are usually happy after drinking the potion, but that's because they were happy before: the Gauls take the potion before fighting, and they love fighting. I can't recall the book(s) offhand, but I do remember Astérix being annoyed at an adversary (a Roman?) who is obstructing him, drinking some potion, and thumping away the obstruction. This doesn't make him feel any less annoyed, it just removes an obstacle that was in the way. This is completely different from methamphetamine, which as I understand it enables feats of strength because it allows one to ignore the limiting feedback from one's body.
The Gauls are depicted as enjoying life. They are the very picture of bons vivants. They don't need drugs for that.
Violence in Asterix is always sanitized. Pain is only conveyed discretely if at all and injuries only last a few panels. Nobody dies from having their head bashed into a wall. This is true even in Asterix and the Roman Agent (La Zizanie) and Asterix and the Great Divide (Le Grand fossé), both of which can be said to criticize violent conflict. Asterix is never about the horrors of war.
In French culture, the use of methamphetamine in war is little known: it's primarily known for its use for doping in sport and by students who want to stay awake. As far as I know, amphetamines were not in common use in the French army, unlike German, Italian, US and British armies. At least that's what I gather from French language sources (e.g. article in Le Monde mentioning only German and British trooes, not French troops; modern article published by the French army discussing historical use during WWII by German, British and US troops, but not by French troops, and stating that the French army today doesn't use them). It is unlikely that a French author would have associated amphetamines with war.
In Goscinny raconte les secrets d'Astérix (René Goscinny, Cherche Midi, 2014), René Goscinny, the writer of Asterix, briefly discusses the origin of the magic potion. My translation:
As for the magic potion that grants the indomitable Gauls superhuman strength, it was only meant to appear in the first episode. But it had so much success that we kept it. (…) The magic potion is something I use to show that our wars are not serious, since all it takes to make everything better is a sip of a drink.
So the intended narrative goal is also completely different.