Niraj Naik, who runs a blog called the The Renegade Pharmacist , claimed the low calorie fizzy drink rots teeth, encourages the body to pile on fat and even mimics the effects of cocaine.
He has drawn up a timeline detailing the effects of swigging a can of Diet Coke, which is marketed as a healthy alternative to full-fat, sugar-packed Coke.
The pharmacist's warning comes after he released an infographic about the dangers of Coke , which quickly went viral across the world.
"From my experience as a community pharmacist helping people to get off medications for metabolic diseases such as heart disease, diabetes and obesity, I found if people drink diet sodas they still get the same problems as people who drink normal soda," Naik claimed.
When you first swig a can of diet coke, Naik alleged, phosphoric acid begins to attack your teeth.
The chemical aspartame then "trigger taste receptors and trick your body into thinking it has just processed sugar"
Then, 40 minutes after the drink, Diet Coke may have turned the drinker into an addict, the pharmacist suggested.
"The potentially deadly combination of caffeine and aspartame creates a short addictive high similar in the way cocaine works," Naik wrote.
"Excitotoxins are released which may exhaust your brain by overstimulating it’s neuroreceptors, especially if consumed on a regular basis."
"Unlike the small amount of satisfaction you get from regular coke your body may still crave sweets," the pharmacist added.
"This makes you likely to reach for another soda, or worse, some other junk food you consider to be safe and the cycle continues."
He warned a can of Diet Coke provides "no nourishment" and "will never quench your thirst as it dehydrates rather than hydrates your body".
So what about the claims the lighter version of Coke can help lose weight?
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"Artificial sweeteners are associated with a drop in the appetite-regulating hormone leptin," she said.
"Leptin is the hormone that inhibits hunger so diet drinks like Diet Coke actually make you hungry and less satisfied with normal amounts of food, and finally when you eat or drink a lot of chemicals that your body simply cannot break down, your body makes more and more internal fat to wrap the chemicals in keeping those harmful chemicals away from your vital organs.
"As Diet Coke has no calories and no recognised ingredients we know it is a cocktail of chemicals that encourage your body to gain and store weight especially on your legs and bottom away from your organs. Diet drinks are not good for your body your health or even as it turns out, for dieting."
Previous research found a "striking'" relationship between consumption of diet drinks and widening waistbands among the over-65s.
We have contacted Coca Cola for comment.