On average, chlorhexidine mouthwash (CHX) should be used for 2 weeks at most unless otherwise directed by your dentist.
The two major reasons for the 2 weeks time limit are due to the maximum dosage size and potential adverse effects from long term use. While this medicated mouth rinse isn't harmful per say, it does come with some undesirable side effects.
Maximum dosage size
On average, most dentists licensed in the US will tell their patients that they should use chlorhexidine mouthwash for two weeks at most. This recommendation is what we were taught in dental school and consequently what our colleagues all abide to.
Perhaps it's not so obvious but the maximum dosage size for a prescription bottle of chlorhexidine gluconate oral rinse is 473 mL. The significance of that number is that when you use the CHX mouthwash as directed, it gives a maximum of two weeks of use!
Fill the cap to the "fill line" which is 15 mL.
Swish around in mouth for 30 seconds undiluted.
Spit out and do NOT rinse with water immediately afterwards.
Use twice a day (after breakfast and before bed).
Evidence of 2 weeks maximum use
Now, let me do some math to prove to you that you only get 2 weeks of use.
Standard size bottle of CHX = 473 mL
Use twice a day with 15 mL each time = 30 mL total per day
473/30 = ~15 days of use
In summary, a full bottle of chlorhexidine oral rinse will last you approximately 2 weeks. Therefore, if you were prescribed a bottle of CHX, you'd only be able to use it for 2 weeks at most because of the dosage size and bottle size limitation.
The only way to use chlorhexidine for longer than 2 weeks is if you have a prescription refill.
Chlorhexidine adverse effects
One of the main hesitations in using chlorhexidine gluconate oral rinse long term is due to it's staining potential. It can cause brown discolorations to your teeth, tongue, and dental fillings.
Even if you're not actively whitening your teeth at the moment, nobody wants their teeth to purposely become more yellow in color. The risk of teeth staining from chlorhexidine use only increases the longer that you use it.
Therefore in order to minimize staining, you should only use it for a short period of time.
Staining mechanism
Chlorhexidine mouthwash does not directly stain your teeth but it makes them more prone to staining. Research has shown that after rinsing with CHX, teeth become more strongly attracted to colored dyes.
That means if you eat or drink stainings foods, they will become more potent at discoloring your enamel than they normally would.
The cause for this strong attraction has to do with the fact that CHX is positively charged while stain molecules tend to be negatively charged. As we all know, opposites attract!
How to remove the stains
Fortunately, chlorhexidine stains can be removed by having your teeth professionally cleaned and by using whitening products. Yes, even the CHX stains on your tongue can be removed as well.
The instructions on the label do say that good oral hygiene can help minimize the discolorations. That means you should be extra diligent while you're using this rinse.
Is it safe to use?
CHX mouthwash is relatively safe to use due to its poor absorption across membranes so its plasma levels are typically undetectable. Most of it is eliminated through feces (~90%) and less than 1% is excreted through urine.
In other words, even if some of it was ingested most of it would simply pass through your gastrointestinal tract. Most of CHX would just get pooped out without much of it being absorbed into your bloodstream.
Since our bodies can't really process and absorb it, that makes chlorhexidine relatively safe to use. However, you do have to be cautious in that while the CHX is poorly absorbed, there are other ingredients which may induce side effects such as the 11.6% alcohol content.
Alcohol content
Due to the alcohol content in CHX, if you accidentally ingest it, you may experience nausea and vomiting. Overall you'll get symptoms similar to inebriation. These side effects are nearly identical to if you swallowed one of the alcohol based essential oil mouthwashes like Listerine.
One of the reasons as to why the CHX oral rinse isn't recommended in those age 18 and under is partly due to the alcohol. Unless specified by your doctor, please keep it out of reach for those who are underaged.
Long term chlorhexidine use
Chlorhexidine gluconate oral rinse is mostly used for short durations of time such as 2 weeks. In the UK, it is licensed for 30 days of maximum use.
Reasons for short term use:
Adverse cosmetic effects such as staining.
It is an adjunctive treatment and not the primary one.
Since it is an antimicrobial rinse, it can induce antibiotic resistance for bacteria.
Due to all of the reasons above, it is not recommended to use chlorhexidine long term. However, there are always exceptions.
Exceptions
There are certain conditions which may require more frequent use of chlorhexidine oral rinse. When we say frequent, we mean that you may get a prescription for it more than once per year but you're still not using it every day. Therefore you're just using it more than the average person but still not as an everyday mouth rinse.
Conditions which may require more frequent CHX use:
Severe periodontal disease
Mouth full of implants
Typically it would have to be extenuating circumstances for your dentist to even consider this as an option. After all there are a lot of other great mouthwashes out there that don't require a prescription and they come with less adverse effects.
The Verdict
Chlorhexidine mouthwash should only be used for as long as 2 weeks because the size of the bottle only permits that many uses. Aside from that, most people really don't want to use this medicated oral rinse long term due to its adverse cosmetic effects.
However, if you were directed by your dentist to use it for longer than 2 weeks, you may do so. If this is your case then you most likely have an extenuating circumstance.
Nonetheless, the most common reason to be prescribed it is after a deep teeth cleaning and you really only need to use it for 2 weeks!
