# L-lysine side effects



## Marcia (Dec 26, 2010)

I was cruising through this pet guide and came across this article about lysine in cats. Then came across the part about side effects. I had no idea there were any!! 

From the article: 

_*Some cats are highly sensitive to this drug and may exhibit symptoms like facial swelling, hives, diarrhea, persistent scratching, vomiting, pale gums and seizures after having lysine. Lysine is also known to react with vitamins, and other supplements. In fact, if the drug is given in large doses, the cat can develop toxicity to other antibiotics like gentamicin, tobramycin, amikacin, kanamycin, neomycin, streptomycin and other penicillin-based drugs. Hence, if your cat starts vomiting or biting its stomach, it should be instantly taken to a veterinarian as this can be a case of an upset stomach or some severe infection.*_
Read more at Buzzle: http://www.buzzle.com/articles/lysine-for-cats.html

I've been an advocate of lysine use because of the ongoing issues with Missy and Lacey but never considered there my be side effects - some serious to it's use.


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## snowy (Aug 23, 2012)

I have only read that high dose of L-lysine can cause a depletion of L-arginine. This is new, thanks for sharing.


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## 10cats2dogs (Jun 16, 2013)

WOW! Marcia, I give my cats l-lysine too...
First time I've heard about side effects for cats...
Good Info! Thanks for sharing!
Sharon


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## doodlebug (May 13, 2006)

The article is written by someone who has no veterinary background. I have found a couple articles that indicate there can be problems at "large" doses, but they don't indicate what a large dose is. The following 2 sources, which are much more reputable, imo, indicate that a dose as high as 1000 mg per day has no known side effects. 

http://www.winnfelinehealth.org/Pages/winn_Seminar_maggs_final_by_Wolf_web.pdf

Feline Herpesvirus - Eye Care for Animals


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## 10cats2dogs (Jun 16, 2013)

Thanks Doodlebug for clearing up this issue! Its good to be a bit cautious and I do know that even people can go overboard on vitamins and stuff!!


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## NOLAKitties (May 30, 2013)

For l-lysine I only give it only when the cat needs it and always at a smaller dosage. 
Actually I'm in the habit of giving supplements at lower dosage usually half. Some of their food already contain omega-3 so I don't give them fish oil that day. The hairball supplement I cut it in half. Probiotic only a little bit from what the manufacturer recommend. I feel even with lower dosage I already can see the benefit. Only if it doesn't work then I will increase the dosage.


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## laurief (Jun 22, 2008)

According to _Plumb's Veterinary Drug Handbook 7th Edition_ (the drug reference used by most veterinarians):

"Lysine may be effective in suppressing FHV-1 infections in cats. Three recently published studies ..., however, have not shown lysine to be effective to prevent or reduce the recurrence of upper respiratory tract infections in shelter cats and in two of these studies, cats receiving lysine supplementation had increases in disease severity and detection of FHV-1 DNA."

"Lysine is an amino acid that is thought to compete with arginine for incorporation into many herpes viruses. As it is believed that arginine is required for producing infective viral particles, when lysine is incorporated, the virus becomes less infective."

"Adverse effects are unlikely when mixed with food."

"*Overdosage/Acute Toxicity*
Significant toxicity is unlikely. Gastrointestinal effects (nausea, vomiting, diarrhea) may occur."

"The following drug interactions have either been reported or are theoretical in humans or animals receiving lysine and may be of significance in veterinary patients:
**ARGININE*: Arginine may negate the anti-herpesvirus effects of lysine
**CALCIUM,ORAL*: Concomitant use with calcium supplements may increase calcium absorption from the gut and decrease calcium loss in the urine"

Recommended feline doses range from 250mg by mouth once daily to 500mg by mouth twice daily for life. Dosing information is provided only for herpesvirus ocular and dermatologic infections. 

It is noted to avoid purchasing lysine products that contain propylene glycol.

Laurie


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