Even though I haven't personally used Grow Taller 4 Idiots (I'm 5"11 and fine with that) I wanted to try to answer your question in the hopes that it will help you make a decision about whether or not to try this program. I wanted to put together some pluses and minuses to the idea.
The Grow Taller 4 Idiots program is not dangerous, at least not from what I can see. It is comprised of essentially four pieces of "therapy" that make a logical sort of sense.
- Stretches -- The spine is often compressed (not a scientific explanation, but an understandable one.) By doing the proper stretches you can put it back into the correct shape and gain height this way. I suspect it is similar to what a chiropractor can do, but here you can do it yourself. You are not actually growing, per say, but you are sort of expanding yourself. This, to me, makes a certain logical sense and I would suspect any gain in height would depend on how long you kept doing the stretches as your spine would want to go back to its old shape. People seem to think you can gain between 1/2 inch and 2 inches this way, but it depends on the individual.
- Posture -- By practicing good posture you will learn to stand up straighter, which will make you taller. The program shows you some facts about bad posture. This, too makes sense. Stand up straighter and you will be taller.
- Nutrition -- Vitamins and nutrition play a big role in height. I know this is true, but in the Western World very few people (in my opinion) suffer from a true deficiency in vitamins that would inhibit growth. There are extreme cases of malnourished children who grow by leaps and bounds when fed properly but most of us, though we may have a cruddy diet, don't count as malnourished in this sense. That said, learning more about nutrition and growth won't hurt you.
- Sleep -- This program has information about how to sleep so that your back is in the right position. Again, this isn't really making you grow, but keeping your spine in the correct alignment to maximize the height you already have.
There is more to the program, but those are the main points. As you can see, I suspect that this program would make you taller by a few inches, but not by making you grow. I suspect most of the change would come from correcting problems you don't know you have.
There are some things I don't like about this program.
- It is informational. $50 or so seems like a lot of money to buy information you could probably find on the web for free (stretches and such.)
- The advertising is, in my opinion, "emotionally loaded" and misleading.
Take a look at some of the phrasing they use:
cursed by your inherited small stature
Missing out on your life-long dreams to becoming a professional athlete
Getting overlooked for job opportunities such as being a runway model
Being carded and questioned about your age, which is embarrassing
Not attracting the girl (or guy) you desire because they choose to date someone... “Taller?”
Are shorter people really "cursed?" Are people that short really dreaming of being "runway models" instead of just regular models? Is a few inches in height going to suddenly make you a great athlete? And for every guy who likes tall girls, there is another who loves adorable short ones.
Basically, if you have $50 this program won't hurt, and it might squeeze out a couple extra inches for you, but make sure you're doing it for the right reasons.