It is generally thought that a desire to eat chalk is an indication of a calcium deficiency, so it is advisable that you visit a doctor for a check up as soon as possible. A calcium deficiency is not a medical emergency or even close to it, but it can certainly cause a lot of problems in the long run, and it is better to get it addressed as soon as possible, especially since the problem can be solved quite easily. However, although eating chalk tends to be associated with a calcium deficiency in the minds of most lay people, the habit is more often an indication of a deficiency in iron or zinc. Whatever the case may be, your doctor will help you determine what the cause is.
What you are suffering from is actually a recognized medical condition that is known as "pica". It basically involves a desire to eat substances that are not normally consumed by humans - mud, paper, coal, ash, chalk, and so on, of which chalk is particularly common. The harmful effects depend on the substance that is eaten. Eating substances such as mud carries a high risk of worm infections and poisoning from various toxic substances. Fortunately for you, chalk is not particularly harmful when consumed. This does not however mean that it is safe - chalk does contain other added chemicals that are not fit for human consumption, and in addition, the chalk powder can cause respiratory problems in the long run.
Determining and addressing the nutritional deficiency that is causing you to eat chalk is the best way to stop the habit. Of course, you need to exercise some amount of will power, but once you no longer have a deficiency, your body will stop craving chalk, and the habit will stop on its own.
answered by M W