Genetics
Medicine isn't magic. Treatments can't give you superpowers. As TheDemonLord says in their answer, it unlocks strength you already had at best. Unfortunately these limits on your own strength are for good reasons, damaging yourself in the process. You want to be able to be strong or happy the day after as well. With removing these limits, you can't be sure of that at all. Not to mention that the senses are more easily physically capped. Finally, there are good reasons to not mix many drugs. Though I can comfortably tell you, no mix of drugs will give you superpowers, nor will any out of control radiation therapy or the like.
If we're going sci-fi already, I would opt for genetical changes. Not only would this be able to tackle the actual disease, but the scientist can on purpose change the user in different ways. Nature has evolved to always renew itself to be able to tackle the next challenge the environment throws in nature's way, removing the need for life longer than one or a few times reproduction. In addition, it is survival of the fittest,not strongest. Nature saves energy where it can, which is why muscles atrophy when not used, or memories fade.
With genetics you could, theoretically, control it all. You can remove the limits or reduce other effects. Atrophy of the muscles slowed down to a crawl. Muslce growth becomes easy, making 'superhuman' strength feats much more easy. You can start tampering with how the eyes grow, increasing the rods and cones to resemble that of a jumping spider or eagle. You change the brain to (temporarily) be in a state of increased flexibility, like when you were very young, to be able to quickly adapt and learn all the new inputs and outputs, as to not overwhelm the person with new, poorly understood information. Maybe make much of the brain much more dense, as the frontal lobe is more like swiss cheese compared to the brain stem for example.
It would require a knowledge unheard of in science to pull that all off, tailored to the specific person. It wouldn't be a 'take today, resulting tomorrow' thing either. You probably want several phases where growth or changes are induced, capping them later. Many would also require action of the person as well, as for example proper muscle growth is also based on (micro) damages of the muscle cells sustained during activities.
That would mean it is a very intentional act on behalf of the scientist, adding in these changes in the cocktail put into the bloodsteam. The scientist might try to cure the disease as well, but simply not yet be as knowledgeable yet about this specific topic.
