decisive, dramatic, far-reaching, important, marked, powerful, profound, pronounced, significant, strong
marginal, minimal, modest, negligible
main, major, principal
full
The full effects of the new tax have not yet been felt.

no apparent, no appreciable, no detectable, no discernible, no measurable, no noticeable, no visible
The drug was devoid of any apparent effect.
There was no discernible effect on cell growth.

likely, possible, potential, predictable, probable
subtle
disproportionate
residual
adverse, catastrophic, crippling, damaging, debilitating, deleterious, destructive, detrimental, devastating, disastrous, harmful, ill, negative, serious, traumatic, undesirable, unfortunate
the crippling effect of sanctions on the economy
He didn't seem to have suffered any ill effects from his fall.

chilling
It's a policy that will have a chilling effect on free speech.

destabilizing, stabilizing
the opposite
His comment was intended to calm the situation but it had the opposite effect.

unintended
beneficial, positive, salutary
the desired
We had problems with mosquitoes, but this spray had the desired effect.

moderating (esp. AmE)
magical, remarkable
Giving up smoking had a magical effect on his stamina.

immediate
direct, indirect
short-term
lasting, long-term, permanent
domino, knock-on, ripple, spillover (esp. AmE), trickle-down
Any delay in delivery of materials will have a knock-on effect throughout the production process.

practical
aggregate, combined, cumulative, net, overall
deterrent
The deterrent effect of the death penalty has long been questioned.

inhibitory
The drug has well-documented inhibitory effects on sexual function.

calming, hypnotic, sedative, soothing, soporific
therapeutic
protective
placebo
toxic
inflationary
corrosive
greenhouse
policies to reduce emissions of gases which cause the greenhouse effect

bring about, exert, have, produce
The drug exerts a powerful effect on the brain.

take
The medicine started to take effect after a few minutes.

experience, feel, suffer, suffer from
Women feel the effects of alcohol more quickly than men.

recover from
note, observe
detect
demonstrate, exhibit, illustrate, reveal, show
analyse/analyze, assess, determine, estimate, evaluate, examine, explore, investigate, measure, monitor, quantify, study, test
document
I am interested in documenting the effects of international events on ordinary people.

compare
blunt, buffer (esp. AmE), cushion, diminish, lessen, limit, minimize, mitigate, reduce, soften
to minimize the effects of economic change

ameliorate
cancel out, eliminate, negate, nullify
counter, counteract, counterbalance, moderate, neutralize, offset
block, combat, suppress
a face cream designed to combat the effects of age

overcome
reverse
amplify, compound, enhance, exacerbate, magnify, maximize
mimic, simulate
drugs which mimic the effects of hormones

avoid
aim at
That is precisely the effect I was aiming at.

be worried about, fear
overestimate, underestimate
ignore, neglect
predict
describe, explain

exist, occur
spread
last
arise from sth, result from sth
the serious health effects which result from obesity

disappear, wear off
How soon will the effects of the drug wear off?

differ, vary

in effect
The border closure meant, in effect, that no trade took place between the countries.

to this effect, to that effect
They told us to go away, or words to that effect.

with … effect
The plague struck again with devastating effect.

effect on, effect upon
The dry weather had an adverse effect on the potato crops.

cause and effect
key historical concepts such as cause and effect

to little effect, to no effect
The air conditioning came on, to little effect.

immediate

come into
The new regulations come into effect next month.

bring sth into, put sth into
The recommendations will soon be put into effect.

in effect
Some laws from the 18th century are still in effect.

with effect
The bank has cut interest rates with immediate effect.

dramatic, startling, striking, stunning
maximum, optimum
the desired
I found that by adding white I could achieve the desired effect.

overall
The overall effect of the painting is overwhelming.

give (sth), have
The stage lighting gives the effect of a moonlit scene.

achieve, create
enhance, heighten
The dramatic effect was heightened by her black dress and dead white face.

spoil

for … effect
‘You know why I'm here?’ Doug paused for maximum effect.

to … effect
She uses animal sounds to startling effect in her music.

special
cinematic
audio, sound
optical, visual
lighting
elaborate
digital