Manipulation of hormones has been done synthetically with designer drugs and steroids.
In most cases - especially in sports competitions - this is considered to be "unethical" and dangerous.
Some of the effects from the use of these drugs are very intense and impressive and could be classified as "super-human" as they would never occur naturally without their use.
Long term use of some of these drugs even alters genes permanently.
Another example would be the use of mechanical limbs like 'Blade Runner' Pistorius who was disqualified from Olympic competition because his prosthetic(s) were not "natural" and too advanced - giving him an unfair advantage and a "super-human" quality.
Pistorius' prosthetic(s) not being "natural" - as they are mechanical - would also be considered a kind of synthetic manipulation.
The human body is weak. Super healing, strength, flight, speed are all impossible. The human body is about as dense as water and poses nothing super about it except, perhaps its intelligence. The only superhero with superpowers that is physically possible to any degree is "Iron man". Exo-robotics could make a very sturdy, very strong robotic exoskeleton. However, it is impossible to gain superpowers due to any drug or synthetic known.
All around us we have people that use artificial means to have a form of superhuman ability. For instance there is a special pair of spring loaded stilts that allow a person to jump higher than a pro-basketball players, clothing that can make a person bulletproof, and many ways that allow man to fly. For the most part, just having an artificial superpower would not be unethical, what you do with the power is a different story.
I have somewhat conflicting views on this hypothetical matter. Having some type of superhuman ability has been my biggest fantasy for years, so if I was given an opportunity, I would most likely seize it. On the other hand, I ask myself this question: Why should I have it and no one else? If this were to become a scientific project, it would become unethical if pursued for the wrong reasons.
If those three criteria are not infringed upon, you're in the good, mate. ^^ I s'pose I need to fill this up. Obviously, if it's not safe then the people have to know that or else consent was coerced. The people being experimented on have to be sane lest again consent is coerced. Then if they weren't willing in the first place that makes the means unethical despite the way they acquired it.
If the people know it's safe/unsafe and with rational mind accept any risks such experimentation may entail anyway, then synthetically acquired superhuman powers are good to go. Let's do the masochism tango. ^^ I feel the need to say something else.... I'll think of it later.