Whenever I talk about power-suppression drugs, the same question always gets asked: "can the authorities take powers away from villains?"
So far, no. And when it happens, you'll know, because it'll be the biggest news since the discovery of superpowers to begin with. It'll mean calls for legislation to forcibly depower all villains, even those in jail. There'll be pogroms in other countries, riots, news articles, pundits. Everyone will want to control the "problem" (supers), with depowerment the punishment for noncompliance.
Until then, as far as I know, only the heroine Illumina is capable of permanently depowering someone, and even then there are some villains she can't (or maybe won't) depower. Rest assured that the authorities are furiously trying to learn her secret, though. So far, from what I know, she isn't cooperating.
Depowering drugs might be a thing in 20 years or 200. All we know now, thanks to Illumina, is that it's possible. But even then, it's not like Eve-active women will stop giving birth to new supers. Powers - and heroes, and villains - are here to stay.
The legalities of permanent power loss
Furman v. Georgia laid out a four-part test in 1972 for what constitutes "cruel and unusual punishment": whether the punishment degrades human dignity; whether it is inflicted in arbitrary fashion; whether it is rejected by society; and whether it is patently unnecessary.
One depowered villain (the first Blacklight) actually tried to sue the government for sanctioning Illumina's power drain on him. The case was thrown out for technical reasons, but the government's defense was very interesting, and troubling. First, they claimed that since supers were essentially extra-human, the loss of these extra powers did not impinge on basic human dignity. Second, they argued that the punishment wasn't arbitrary, because it followed the conventional pattern of escalation of force that police use every day. Third, they said it wasn't rejected by society because of its novelty (the judge was not amused by this line of reasoning). Fourth, they argued that Blacklight's actions had placed people in jeopardy, and that as a repeat offender it was not "patently unnecessary".
Blacklight's prosecution argued from the Universal Declaration of Human Rights, adopted by the UN in 1948, that depowerment violated the "security of person" the Declaration called for. Whether the government was correct that supers are human plus something else, they said, wasn't relevant. In the country of the blind, the one-eyed man still deserves his one eye.
Aside from this argument, they also tried to refute the government's position about societal rejection by drawing analogies to lobotomies and chemical castration, two techniques that have been used recently to deal with prisoners (criminal or otherwise). They went back further and compared loss of power to amputation.
Overall the government had a good case, though I am certain Blacklight's legal team would have better chances with a more sympathetic (or less biased) judge. That said, I expect that any permanent power loss mechanism will be employed by the government long before the legality of doing so is settled at the national level - it's too powerful a weapon not to use.