Many of the pills around these days are simply packed with stimulants and caffeine. Try not to take these because they can damage your metabolism more than it's worth in the long run. They do speed up your metabolism, but they'll also give you the jitters and often make you a bit edgy. There are much better ways to speed up your metabolism and it's not even all that hard.
Now, the most important thing to remember in your goal to loose weight and build muscle is to do what many bodybuilders and professional fitness trainers refer to as "eating clean".
Simply feed your body the elements it needs to repair itself from the workouts you've been doing. We all know that eating foods like fried chicken and take away fish and chips is not going to give you the quality vitamins and nutrients you need. So what foods should you eat to stay on a "clean diet"?
So what's the most important part of a clean diet? Water!
I know, it's not a food. But it is an essential nutrient and our bodies are made up of more than 80% water. So drink it, lots of it. It's a great cleanser and will aid your body in it's efforts to rid itself of toxic wastes and will also help you loose weight quickly.
Fresh Fruits and Vegetables are the best source of carbohydrates for your body while you're trying to loose weight and build muscle. They'll provide your body with nutrients and energy that's quickly digested so your metabolism will speed up, and you'll feel more alive.
Protein is essential for your body to synthesize new muscle cells. Protein supplements are probably one of the only worthwhile supplements I'd consider buying when you're looking to loose weight and build muscle. It's important to provide a quickly digestible high quality protein to give your muscles what they need to repair and grow quickly, when they need it most, right after training. So get yourself some good quality whey (or soy if you're vegetarian) protein supplement and have a milk shake after you train. You deserve it!
You should eat roughly 5-7 times a day, small meals with a bit of protein in each meal so you don't have cravings. Protein has the ability to stave off sugar cravings so if you get a bit of a sweet tooth, grab another shake (with water), or a protein nutrition bar. Also, a handful of raw nuts is a great substitute.