You actually buy and take some kind of man-made chemical every single day to avoid getting a cold sore every month or two?

Here is the list of known side-effects here (sorry about the formatting but i guess carriage returns don't translate well):

Along with its needed effects, valacyclovir (the active ingredient contained in Valtrex) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking valacyclovir:

More common

Discouragement
feeling sad or empty
irritability
lack of appetite
loss of interest or pleasure
tiredness
trouble concentrating
trouble sleeping
Rare

Black, tarry stools
chest pain
chills
cough
decreased frequency or output of urine
fever
flu-like symptoms
headache
lower back or side pain
reduced mental alertness
shortness of breath
yellow eyes or skin
Incidence not known

Actions that are out of control
agitation
anxiety
back, leg, or stomach pains
bleeding gums
blood in urine or stools
blurred vision
change in consciousness
change in mental status
changes in behavior, especially in interactions with other people
changes in patterns and rhythms of speech
dark or bloody urine
difficult or labored breathing
difficulty speaking
difficulty swallowing
dizziness
drowsiness
dry mouth
fast, pounding, or irregular heartbeat or pulse
feeling that others are watching you or controlling your behavior
feeling that others can hear your thoughts
feeling, seeing, or hearing things that are not there
general tiredness and weakness
hyperventilation
increased thirst
itching
lightheadedness when getting up from a lying or sitting position
light-colored stools
loss of consciousness
mood or mental changes
nausea and vomiting
nervousness
pale color of skin
pinpoint red spots on the skin
pounding in the ears
puffiness or swelling of the eyelids or around the eyes, face, lips, or tongue
redness of the skin
restlessness
seeing, hearing, or feeling things that are not there
seizures
severe mood or mental changes
shakiness and unsteady walk
shakiness in the legs, arms, hands, or feet
skin rash
slurred speech
sores, ulcers, or white spots on the lips or in the mouth
stiff neck
swelling of the face, fingers, or lower legs
swollen or painful glands
talking, feeling, and acting with excitement
tightness in the chest
trembling or shaking of the hands or feet
trouble in speaking
troubled breathing
unsteadiness, trembling, or other problems with muscle control or coordination
unusual behavior
unusual bleeding or bruising
unusual tiredness or weakness
upper right abdominal pain
vomiting
weight gain
wheezing
Some side effects of valacyclovir may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

Body aches or pain
cramps
difficulty in moving
ear congestion
heavy bleeding
loss of voice
muscle aches
muscle pain or stiffness
nasal congestion
pain
pain in joints
sneezing
sore throat
stuffy or runny nose
Less common

Constipation
diarrhea
Incidence not known

Blistering, peeling, or loosening of the skin
hair loss or thinning of the hair
hives or welts
increased sensitivity of skin to sunlight
red, irritated eyes
redness or other discoloration of the skin
severe sunburn
For Healthcare Professionals
Applies to valacyclovir: oral tablet

Gastrointestinal
Very common (10% or more): Nausea (up to 16%)
Common (1% to 10%): Vomiting, constipation, anorexia, dyspepsia, dry mouth, flatulence
Frequency not reported: Tooth disorder
Postmarketing reports: Diarrhea[Ref]

Nervous system
Very common (10% or more): Headache (up to 16%)
Common (1% to 10%): Dizziness, somnolence
Frequency not reported: Migraine
Postmarketing reports: Seizures, tremors, ataxia, coma, dysarthria, encephalopathy[Ref]

Neurologic/psychiatric events, sometimes severe, have included confusion, agitation, convulsions, hallucinations, and coma have generally been reversible with discontinuation. These events have mostly been seen in patients with renal impairment or in patients receiving higher doses.[Ref]

Psychiatric
Neurologic/psychiatric events, sometimes severe, have included confusion, agitation, convulsions, hallucinations, and coma have generally been reversible with discontinuation. These events have mostly been seen in patients with renal impairment or in patients receiving higher doses.[Ref]

Common (1% to 10%): Depression, insomnia
Postmarketing reports: Aggressive behavior, agitation, confusion, mania, psychosis, auditory and visual hallucinations[Ref]

Renal
Uncommon (0.1% to 1%): Increased serum creatinine
Frequency not reported: Acute renal failure
Postmarketing reports: Renal failure, renal pain[Ref]

Hematologic
TTP/HUS, including some fatalities, has been reported during clinical trials in patients with advanced HIV disease and in allogeneic bone marrow transplant and renal transplant recipients, who were receiving 8 g per day.[Ref]

Common (1% to 10%): Decreased neutrophil counts, decreased platelet counts
Uncommon (0.1% to 1%): Decreased hemoglobin
Frequency not reported: Thrombotic thrombocytopenic purpura/hemolytic uremic syndrome
Postmarketing reports: Thrombocytopenia, aplastic anemia, leukocytoclastic vasculitis[Ref]

Hepatic
Common (1% to 10%): Abnormal ALT, elevated alkaline phosphatase, elevated AST
Postmarketing reports: Hepatitis[Ref]

Hypersensitivity
Postmarketing reports: Acute hypersensitivity reactions including anaphylaxis, angioedema, dyspnea, pruritus, rash, urticaria[Ref]

Dermatologic
Common (1% to 10%): Rash
Frequency not reported: Acne, pruritus
Postmarketing reports: Facial edema, erythema multiforme, photosensitivity, alopecia[Ref]

Cardiovascular
Postmarketing reports: Hypertension, tachycardia[Ref]

Ocular
Postmarketing reports: Visual abnormalities[Ref]

Respiratory
Common (1% to 10%): Nasopharyngitis, upper respiratory tract infection, rhinitis, pharyngitis
Uncommon (0.1% to 1%): Dyspnea
Frequency not reported: Sinusitis, bronchitis[Ref]

Musculoskeletal
Common (1% to 10%): Arthralgia
Uncommon (0.1% to 1%): Back pain[Ref]

Genitourinary
Frequency not reported: Dysmenorrhea, urinary tract infection[Ref]

Other
Common (1% to 10%): Fatigue, asthenia, fever, chills[Ref]

General
The most commonly reported adverse reactions have been headache, nausea, and abdominal pain.[Ref]

References
1. "Product Information. Valtrex (valacyclovir)." Glaxo Wellcome, Research Triangle Park, NC.

2. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0

3. Cerner Multum, Inc. "Australian Product Information." O 0