This is info I found here:
hcgdietinfo.com/hcgdietf
orums/f35/read-first-what-
cycling-13278/
It's something I've been interested in doing for awhile. I'm debating on trying this...remember I can't take credit for the info it is from the above url.
If anyone has any thoughts I'd be interested in hearing them!

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What is cycling?

In a nutshell, cycling is following Dr. Simeons’ protocol and rotating back and forth between P2 and P3 without doing a P4.

Cycling is not for newbies, but for those who have completed at least one full round.

Traditional P2 & P3
The length of a traditional P2 is a minimum of 23 days also known as a short round. Days 1 and 2 are loading days followed by days 3 through 23 of VLCD (very low calorie diet) during which time you are taking hcg. After this point you stop the hcg, but continue with the VLCD for 72 hours if taking Rx hcg, or 48 hours if taking homeopathic hcg, before you start the P3 break.

The length of a traditional P3 is 21 days. During this time, you may eat anything you wish except sugar and starches. You will be stabilizing during this phase. At any point you go over 2 pounds of your LIW (or LDW), you must do a steak day the next day to drop your weight back down within the 2 pound range.

Non-Traditional P2 & P3
Cycling can be modified to fit what works for you. For example, a 2 week /1 week round looks like this:
•2 weeks of P2: day 1 = first injection and load day followed by 13 days of VLCD
•Continue VLCD for 72 hours with no injections - days 15-18
•4 days of P3 - days 19-21
•Cycle back to P2

While cycling, I typically load by eating P3 foods (aka a Mini-Load) and don‘t restrict the amounts; however, I don‘t do a traditional load day wherein I eat any and all foods to capacity and then some. I only load one day at the most. Some people do the traditional 2 load days and eat everything they wish, but realize if you do this, you will have to use extra days of your P2 to lose the load weight.

The key is to pay attention to your body to know what works for you. One thing you must know is this: cycling is not a way to lose more weight in a shorter amount of time. Your losses will not be greater, so if that is your objective for trying cycling, you will be disappointed. Keep in mind when doing shorter rounds, any cheat will effect the result of your round so staying on protocol is imperative because there are not extra days to recover from the cheat. Of course, you can always extend the round if you wish, but then you're likely doing a full P2.

It is recommended that before cycling, a dieter should do a complete round (P2, P3 & P4) before cycling (see Pounds and Inches for pertinent data--at the very least, you should do a full 23 days the first time). Also the last round should be a complete round as well. There are those who have been successful cycling without ever doing a P4 until their last round--this is a decision you will have to make after weighing the facts.

Although similar, cycling is not the same as a “planned interruption” as described in Pounds and Inches. A planned interruption still assumes the dieter will continue to complete a full round including P4.

A final word… cycling is not protocol and it does not work for everyone. You will read arguments both for and against cycling--at this time, there is no definitive information to know the long-term results. Again, it is a personal choice and doing your due diligence is strongly suggested.

Be sure to read Dr. Simeons’ Pounds and Inches to understand the protocol -------------------------